It is well known to utilize a ventilator, anesthesia machine, or pressure support device or other system to deliver a fluid, such as oxygen, air, or other breathing gas or gas mixture, to an airway of patient to augment, supplement, or substitute the patient's own ventilatory effort and/or to treat the patient with a pressure support therapy. Of importance in using such situations is the ability to accurately regulate or control the pressure, flow, and/or volume of gas delivered to the patient. This requires being able to accurately monitor the operating parameters of the ventilator, such as the pressure and/or flow of gas in the ventilator. For present purposes, the term “ventilator” is used to describe any system or device that delivers a flow of gas or pressurized gas to the airway of a user, either invasively or non-invasively, alone or in combination with other systems.
As shown in FIG. 1, the inspiratory related components of a conventional ventilator 20 includes a source of a first gas 30, such as air, and a source of a second gas 32, such as oxygen. The source of first gas typically includes a pressurized storage tank, blower, bellows, impeller, fan, piston, pressure generator, or the like, that provides pressured air at a pressure above ambient pressure. The source of oxygen is typically a pressurized oxygen storage tank, a central wall supply (typically found in a hospital), or an oxygen concentrator. In short, the sources of the first and second gas can be pressure generators that operate under the control of the ventilator, an independent gas supply, such as that available through a hospital's central gas delivery system, or a combination thereof.
A first valve 34 control the supply of the first gas (e.g., air) and a second valve 36 controls the supply of the second gas (e.g., oxygen). The separate gas supplies are mixed downstream of the valves, typically using a mixing element or accumulator, for subsequent delivery to the patient via the inspiratory limb of a patient circuit. The combined gas flow is carried by a primary conduit 42 to an external coupling provided on the ventilator housing. A flexible hose or patient circuit (not shown) couples to the external coupling an airway of the patient. Valves 34 and 36 are typically proportional valves the are opened or closed based on the direction that current flow through the valve, which is a function of the voltage applied across the valve.
The illustrated conventional ventilator includes a first flow sensor 44 adapted to measure a flow of the first gas and a second flow sensor 46 adapted to measure the flow of the second gas. A pressure sensor 48 measures the pressure of the gas in conduit 42 delivered to the patient via the patient circuit. In addition, and oxygen concentration monitor 49 measure the concentration of oxygen in the gas delivered to the patient. The outputs of flow sensors 44 and 46, pressure sensor 48, and oxygen monitor 49 are provided to a controller 50. The controller typically uses this information, at least in some ventilation modes, to control the flow, volume, and/or pressure of gas delivered to the patient, i.e., to control valves 34 and 30 and/or the actuation of the gas sources 30 and/or 32 so that the desired flow, pressure, or volume of gas is administered to the patient having the desired oxygen concentration.
The expiratory components of a conventional ventilator include a expiratory conduit 60 that is coupled to the expiratory limb of the patient circuit. In a conventional setup, the inspiratory limb and the expiratory limb are coupled near the patient at a Y-connector (not shown). The expiratory limb carries gas from the patient back to the ventilator. An expiratory valve 62 that operates under the control of the controller is coupled to conduit 60 to control the release of gas from the conduit into the atmosphere. Sensor, such as a pressure sensor 64 and/or a flow sensor 66 are provided to measure the pressure and/or flow of gas in the expiratory conduit.
A frequently occurring problem with conventional ventilators is that, when a ventilator has to be attached to a patient in an emergency, the ventilator may have a reduced accuracy during a period of time after the start-up of the ventilator. This period of reduced or impaired operating ability can last as long as half an hour of the treatment is started. This problem is of particular importance when ventilating children, and, in the worst case, the patient can be injured as a consequence of the ventilator delivering incorrect flows and/or pressures to the patient. One reason the ventilator may operate with a reduce or impaired ability at start-up is due to heating-up related phenomena that is inherent in the sensing elements of the ventilator, such as the pressure sensors, flow sensors, oxygen concentration sensors, temperature sensors, that are used to monitor one or more characteristics associated with the flow of the gas delivered to or received from the patient.
Conventional ventilators also typically use multiple electronic components, such as flow regulators (valves), sensors (pressure, flow, gas concentration, temperature), processors, etc, that do not operate at the same voltage or current level, i.e., the valves have different power requirements. FIG. 2 is a schematic representation of a conventional ventilator that includes a common power supply of 12 V. In this example, valves 70 and 72 operate at ±12 V. These valves correspond, for example, to one or more of valves 34, 36, and 62 used in the ventilator of FIG. 1. To provide ±12 V to the valves, switched converters 74 and 76 used to switch the 12 V to be provided to the valve between +12 V and −12 V. Other components of the ventilator have other power requirements. For example, processor or controller 50 operates at a voltage level of 3.3 V. A voltage converter 78 converts the 12 V to 3.3 V for use by the controller. In this example, sensors 82 and 84 operate at voltages of ±5 V. These sensor correspond, for example, to any one of the sensors used in the ventilator, such as flow sensors 44, 46, and 66, pressure sensors 48 and 64, and oxygen sensor 49. Voltage converters 90 and 92 convert the +12 V to +5 V, and inverters 94 and 96 are provided to so that both +5 V and −5 V are available for such sensors. Of course, a single voltage converter and single inverter can be used to provide the ±5 V.
When a ventilator requires multiple voltages, there is a challenge in ensuring that the signal/noise-ratio of the various power supplies is kept to an acceptably low level. This is especially difficult in an environment where switched converters are used, because such components include rapidly actuated switches that can induce voltage spikes and other transient noise in the power supply system. For example, noise in the power supply can interfere with pulse width modulated signals used to control the valves or can interfere with the signals provided by the sensors. In a worst case scenario, the interferences can cause inadvertent actuation or deactivate of a ventilator valve used to control the delivery of gas to the patient.
Another problem with ventilators that require multiple voltages is the fact that each voltage source requires separate testing and monitoring in order ensure that each voltage source is providing the correct voltage within a specified tolerance range. This testing and accuracy especially critical in medical equipment, where a patient's health could be impacted by faulty power supplies. A further problem associated with need to use multiple voltages is that a start-up and shut-down, power must be provided to or removed from the various components of the ventilator in a predetermined must sequence. This is necessary to ensure that the components are not damaged during power on or power off. It can be appreciated that the need to control and/or monitor the sequence in which power is provided to or removed from the electronic components of the ventilator leads to high costs in the design of the ventilator and complicates its operation.
One way of reducing the number of voltages is to generate these voltages internally in the ventilator on a module specifically provided for this task. In certain cases, e.g., when generating negative voltages, some form of switching is required, i.e., inductively or capacitively, which leads to undesired disturbances in the power supplies. As noted above, these undesired disturbances may impair the accuracy of the voltage provided to the various electronic components of the ventilator.